The present invention generally relates to radio frequency (RF) trainable transmitters that are capable of learning the characteristics of a received RF signal, storing the characteristics in memory, and re-creating and transmitting the learned signal based upon the stored characteristics.
RF trainable transmitters have many applications. The primary application is to physically and permanently incorporate the trainable transmitter in a vehicle accessory, such as a visor, rearview mirror, or overhead console, in order to allow the trainable transmitter to be used to learn a garage door opening RF signal for subsequent transmission to the garage door opening mechanism mounted in a garage. As disclosed in U.S. Pat. No. 5,903,226, another application of RF trainable transmitters is to control household lights and appliances.
RF trainable transmitters are capable of learning the RF carrier frequency, modulation scheme, and data code of an existing portable remote RF transmitter associated with an existing receiving unit located in the vehicle owner""s garage. Thus, when a vehicle owner purchases a new car having such a trainable transmitter, the vehicle owner may train the transmitter to the vehicle owner""s existing clip-on remote RF transmitter without requiring any new installation in the vehicle or home. Subsequently, the old clip-on transmitter can be discarded or stored.
Because the trainable transmitter is an integral part of a vehicle accessory, the storage and access difficulties presented by existent clip-on remote transmitters are eliminated. Some examples of trainable transmitters are disclosed in U.S. Pat. Nos. 5,442,340; 5,479,155; 5,583,485; 5,614,885; 5,614,891; 5,619,190; 5,627,529; 5,646,701; 5,661,651; 5,661,804; 5,686,903; 5,699,054; 5,699,055; and 5,708,415, as well as in U.S. Pat. Nos. 5,903,22 and 5,854,593, all of which are commonly assigned to Prince Corporation.
A block diagram representing a typical RF trainable transmitter is shown in FIG. 1. As described in more detail below, the RF trainable transmitter includes a signal generator 10 for generating the signals to be transmitted and for generating a reference signal used during the training process to identify the RF carrier frequency and to demodulate the received signal. Signal generator 10 operates under control of a microprocessor 16, which selects the carrier frequency of the signal generated by signal generator 10 by applying a signal frequency control signal to input terminal b of signal generator 10. Microprocessor 16 may also cause signal generator 10 to modulate the generated signal in accordance with a DATA signal applied to input terminal a of signal generator 10. When transmitting a modulated signal, signal generator 10 outputs the modulated signal to a transmit amplifier 27 through output terminal d. The modulated signal is thus amplified and passed to an antenna 2 that transmits the RF signal as signal B to a remotely controlled apparatus 6.
When the trainable transmitter is receiving a signal A from an original remote control transmitter 4 during the training mode, the received signal is fed from antenna 2 to an input of a mixer 8. A reference signal output from terminal c of signal generator 10 is supplied to a second input of mixer 8. Mixer 8 mixes the reference signal and the received signal A to generate a mixed output signal. The mixed output signal passes through a bandpass filter 12 and a processing circuit 14 to an input of a microprocessor 16 where it is further processed.
The RF trainable transmitter also includes user input switches 18 coupled to microprocessor 16 through a switch interface circuit 20, to allow the user to initiate either training of a signal or transmission of a signal. Additionally, one or more light emitting diodes (LEDs) 22 or some other display or indicator circuit may be coupled to an output of microprocessor 16 to provide feedback information to the user. The RF trainable transmitter also includes a power supply circuit 24 that may be permanently or detachably coupled to the battery of a vehicle.
The RF trainable transmitter shown in FIG. 1 typically operates in either a training mode or a transmit mode. To cause the trainable transmitter to enter the training mode, a user presses one of switches 18. Upon detecting that a switch 18 has been depressed for a predetermined time period, microprocessor 16 enters the training mode. During the training mode, the user activates original remote control transmitter 4 associated with a garage door opening mechanism (e.g., remotely controlled apparatus 6) to cause original remote control transmitter 4 to transmit the signal to be learned (A). While signal A is transmitted, microprocessor 16 first identifies the carrier frequency of signal A.
To identify the RF carrier frequency of the received signal, microprocessor 16 generates and supplies a frequency control signal (FREQ) to input terminal b of signal generator 10. Signal generator 10 responds to the frequency control signal by generating an unmodulated RF reference signal having a frequency dictated by the frequency control signal received from microprocessor 16. Antenna 2 supplies the RF reference signal to mixer 8, which mixes the reference signal with the received signal A. Mixer 8 outputs a signal including the data code encoded in the received RF signal and having a carrier frequency that is equal to the difference between the carrier frequencies of the received RF signal and the RF reference signal. Narrow bandpass filter 12 is provided to pass a signal only when the carrier frequency of the signal from mixer 8 is 10.7 MHz. The output of bandpass filter 12 is passed through a processing circuit 14 back to microprocessor 16. In this manner, microprocessor 16 can selectively vary the carrier frequency of the RF reference signal output from signal generator 10 until a signal is detected from processing circuit 14. When a signal is detected from processing circuit 14, microprocessor 16 will know that the carrier frequency of the received RF signal is 3 MHz different from the known carrier frequency of the RF reference signal. Once microprocessor 16 identifies and verifies the carrier frequency, it stores the value of the frequency control signal in its internal memory and digitizes and stores the data code that is demodulated by processing circuit 14.
Subsequently, when a user wishes to cause the trainable transmitter to transmit a signal (B) to the garage door opening mechanism 6, the user presses the associated switch 18 to instruct microprocessor 16 to begin transmitting the RF signal. Microprocessor 16 responds by reading the frequency data from its memory and providing a corresponding frequency control signal to signal generator 10, while also reading from its memory the data code at the same rate at which it was recorded and supplying this data signal (DATA) to input terminal a of signal generator 10. Signal generator 10 then generates a carrier signal having the selected frequency and modulates the amplitude of the signal with the data signal supplied from microprocessor 16. This modulated RF signal (B) is output through antenna 2 to the remotely controlled garage door opening mechanism 6. It should be noted that a plurality of switches 18 is provided to enable a plurality of signals to be learned and subsequently transmitted.
An early version of an RF trainable transmitter is disclosed in U.S. Pat. No. 5,614,885. In this version, signal generator 10 was generally constructed as shown in FIG. 2. Specifically, signal generator 10 employed a voltage controlled oscillator (VCO) 110, which generates a sinusoidal signal having a frequency dictated by the analog voltage level applied at its voltage control input terminal. To allow microprocessor 16 to control the voltage level applied to the voltage control input of VCO 110 using a digital value that may easily be stored in its memory, the output of VCO 110 is fed back through a divide-by-128 circuit 111 as well as a divide-by-N circuit 112 and is mixed by mixer 114 with a reference signal of fixed frequency as generated by a reference oscillator 113. The value of N by which divide-by-N circuit 112 divides the frequency of the signal supplied thereto is provided from microprocessor 16. The output of mixer 114 is supplied to a frequency discriminator circuit 115 that converts the received signal to a voltage signal that has a level corresponding to the frequency of the signal output from mixer 114. Thus, by changing the value of N, microprocessor 16 can effectively adjust the voltage level input to VCO 110 and thereby select the frequency of the signal output from VCO 110.
To modulate the signal output from VCO 110, a switching transistor 116 is provided between the output of VCO 110 and antenna 2. Switching transistor 116 is switched on and off in response to the data signal supplied from microprocessor 16. In this manner, an amplitude-modulated (AM) signal may be generated and supplied to antenna 2 for transmission to the garage door opening mechanism 6.
A problem with the implementation shown in FIG. 2 results from the fact that VCO 110 continuously generates signals during a transmit mode even during those periods when switch 116 is nonconductive. When VCO 110 continuously generates a signal, an AC signal is continuously transmitted through the wiring of the circuit, which tends to operate as a secondary antenna thereby transmitting RF signals when no signal is supposed to be transmitted. To better understand this phenomenon, the construction of VCO 110 is described in detail below.
FIG. 18 shows the general construction of VCO 110 as used in the circuits shown in FIGS. 2 to 4. As shown, VCO 110 includes an oscillator 125 that generates a periodic signal having a frequency that varies in proportion to a voltage applied to terminal 126. Terminal 126 is coupled to oscillator 125 via a resistor 127. The output of oscillator 125 is applied to the base of a transistor 129. As an oscillating output signal from oscillator 125 is applied to the base of transistor 129, transistor 129 generates an oscillating current Ios (see FIG. 19) that in turn is passed through antenna 2 and the other components 130 of the trainable transmitter (see FIG. 19). The current draw of a signal generator 10 including such a VCO 110 is in the relatively high range of 110 to 115 mA. As a result of the relatively high oscillating frequency Ios passing through the wires of signal generator 10 and other portions of the trainable transmitter, a residual radiation is generated by VCO 110 during all periods in which it is operating. Consequently, a trainable transmitter constructed utilizing the signal generator shown in FIG. 2 and having a VCO 110 constructed as shown in FIG. 18 exhibits only 3 to 10 dB pulses, because VCO 110 continuously oscillates during such transmission periods. To overcome this problem, the implementation described in U.S. Pat. No. 5,479,155 and shown in FIG. 3 was adopted.
As shown in FIG. 3, signal generator 10xe2x80x2 similarly includes a VCO 110, divide-by-128 circuit 111, divide-by-N circuit 112, reference oscillator 113, and a mixer 114. These components essentially operate in the same manner as described above. The difference in the two signal generators pertains to the manner in which the generated signal is modulated. To overcome the above-mentioned problem with the implementation shown in FIG. 2, a switching transistor 119 is provided that turns VCO 110 on and off in response to the data signal supplied by microprocessor 16. In this manner, VCO 110 does not generate a signal during the times in which it is not supposed to. However, because the voltage control signal supplied to VCO 110 is dependent upon the feedback of the frequency generated by VCO 110, a loop filter 117 and sample-and-hold circuit 118 are required to prevent the applied voltage from changing as VCO 110 is selectively turned on and off in a transmit mode. If the applied voltage were to change as VCO 110 is turned on and off, the frequency of VCO 110 would become sporadic. The provision of such a sample-and-hold circuit, however, creates other problems, since the capacitor used in the sample-and-hold circuit is relatively large and cannot be incorporated in an integrated circuit. Thus, to overcome that problem, the configuration described in U.S. Pat. No. 5,686,903 and shown in FIG. 4 was adopted.
The configuration shown in FIG. 4 for signal generator 10xe2x80x3 is similar to the prior configuration in that VCO 110 is selectively enabled and disabled in response to the data signal supplied from microprocessor 16. Signal generator 10xe2x80x3 differs from the other signal generator implementations, however, in that a unique phase-locked loop circuit 121 is provided to receive the frequency control signal from microprocessor 16 and to generate the appropriate voltage level to apply to the voltage control input terminal of VCO 110. Phase-locked loop circuit 121 performs this task by comparing the frequency generated by VCO 110 with a fixed reference frequency generated by reference oscillator 113. To prevent phase-locked loop circuit 121 from responding erratically when VCO 110 is disabled, the data signal supplied to VCO 110 is also supplied to phase-locked loop circuit 121 so as to prevent the phase-locked loop circuit from changing the voltage level applied to VCO 110 during such periods that VCO 110 is disabled. A problem with the configuration shown in FIG. 4 is that phase-locked loop circuit 121 must be custom designed to be responsive to the data signal and therefore is more complicated and expensive to produce.
Accordingly, it is an aspect of the present invention to solve the above problems by providing a trainable transmitter that requires fewer parts and is therefore less expensive. An additional aspect of the present invention is to provide a trainable transmitter that has a well partitioned design using bipolar components for the RF circuitry and CMOS components for the microprocessor, thereby utilizing each technology where it is best suited. Yet another aspect of the present invention is to provide a trainable transmitter that operates at current levels of 40 mA or less. Still another aspect of the present invention is to provide a trainable transmitter in which the VCO continuously generates a signal during a transmit mode without causing any residual radiation of significant levels in the frequency bands of interest.
To achieve these and other aspects and advantages, the trainable transmitter of the present invention comprises a receiver for receiving a signal from an original transmitter, a signal generator for generating a signal having a frequency related to a frequency control signal supplied to a frequency control terminal of the signal generator, and a processor directly coupled to the frequency control terminal of the signal generator for supplying the frequency control signal and coupled to an output terminal of the signal generator for monitoring the frequency of the signal output from the signal generator.
The above aspects and advantages may alternatively or additionally be achieved by a trainable transmitter constructed in accordance with a different embodiment in which a transmitter for transmitting an RF signal to a receiver that is responsive to an amplitude-modulated RF signal having a predetermined data code and a carrier frequency within a predetermined frequency band to which the receiver is tuned. The transmitter comprises a signal generator for generating an RF carrier signal having a carrier frequency that is outside the predetermined frequency band of the receiver and a frequency-dividing circuit coupled to an output of the signal generator. When enabled, the frequency-dividing circuit divides the frequency of the RF carrier signal to output a signal having a carrier frequency falling within the predetermined frequency band of the receiver. When disabled, the frequency-dividing circuit passes the RF carrier signal received from the signal generator without dividing its frequency. The transmitter further comprises a control circuit for generating a modulation signal representing the predetermined data code and supplying the modulation signal to the frequency-dividing circuit to selectively enable and disable the frequency-dividing circuit in response to the modulation signal, such that the frequency-dividing circuit generates a modulated RF signal. The transmitter also comprises an antenna coupled to receive the modulated RF signal output from the frequency-dividing circuit and to transmit the modulated RF signal to the receiver.
The above aspects and advantages may alternatively or additionally be achieved by a trainable transmitter constructed in accordance with yet another embodiment in which the trainable transmitter comprises a receiver for receiving a signal from a transmitter, a signal generator including a differential VCO for generating a signal having a frequency related to a frequency control signal supplied to a frequency control terminal of the signal generator, and a control circuit coupled to the receiver and to the frequency control terminal of the signal generator for supplying the frequency control signal so as to control the frequency of the signal generated by the differential VCO.
The above aspects and advantages may further be achieved by a trainable transmitter constructed in accordance with another embodiment of the present invention whereby the trainable transmitter comprises a receiver for receiving a signal from a transmitter, a signal generator for generating an unmodulated signal having a frequency related to a frequency control signal supplied to a frequency control terminal of the signal generator, and a control circuit coupled to the receiver and to the frequency control terminal of the signal generator for supplying the frequency control signal. The control circuit operates in a training mode and a transmission mode. In the training mode, the control circuit controls the signal generator and monitors a connection to the receiver so as to learn characteristics of the received signal, including its carrier frequency. During the transmission mode, the control circuit controls the signal generator to generate an unmodulated signal having the learned carrier frequency while modulating the generated signal after it is output from the signal generator, such that the trainable transmitter transmits a modulated signal during the transmission mode having a signal pulse variation greater than 10 dB.
As described further below, the trainable transmitter of the present invention may be implemented using any one of five different embodiments.